Converting your contact lens prescription to glasses isn't a simple matter of plugging in the numbers. While some similarities exist, contact lenses and glasses sit at different distances from your eye, requiring a slightly different prescription for optimal vision. This guide will walk you through the process, clarifying the nuances and explaining what information you need to successfully get the right glasses prescription.
What Information Do I Need?
Before heading to an optometrist or optician, gather the following information from your contact lens prescription:
- Sphere (SPH): This indicates the power needed to correct nearsightedness (myopia, represented by a minus sign) or farsightedness (hyperopia, represented by a plus sign).
- Cylinder (CYL): This value corrects astigmatism, a refractive error causing blurred vision at all distances. A value of 0.00 indicates no astigmatism.
- Axis (AXIS): This number, ranging from 1 to 180 degrees, specifies the orientation of the astigmatism. It's only relevant if you have astigmatism (CYL is not 0.00).
- Add (ADD): This refers to the additional power added for near vision correction (reading glasses), usually only present in bifocal or progressive lenses. This is not relevant for single-vision contact lenses.
- Base Curve (BC): This describes the curvature of the back surface of your contact lens. This is crucial information and is not directly transferable to a glasses prescription. The optician or optometrist will use this, along with your pupillary distance (PD), to calculate the appropriate lens curvature for your glasses.
- Diameter (DIA): This measures the overall size of your contact lens. While not directly used in glasses prescriptions, it can be helpful for the optometrist to understand your eye size and overall fit.
- Brand and Type of Contact Lenses: Knowing the specific brand and type of lenses you wear helps the professional understand the lens material and its properties, which might influence the glasses prescription.
- Prescription Date: Ensure your prescription is current. Contact lens prescriptions typically expire within a year, and your eyesight might have changed.
Can I Just Transfer the Numbers Myself?
No. While the SPH and CYL values might seem directly transferable, they aren't. The crucial difference lies in the distance between the lens and the eye. Contact lenses rest directly on the cornea, while glasses sit approximately 12-14mm away. This distance impacts the refractive power needed to achieve clear vision. Attempting a direct conversion can lead to inaccurate prescriptions and potentially blurred vision or eye strain.
Why is My Pupillary Distance (PD) Important?
Your pupillary distance (PD) measures the distance between the centers of your pupils. This is essential for accurate glasses prescriptions. An incorrect PD can result in significant eye strain and discomfort. The optometrist or optician will measure your PD, but you can also have it measured at most optical stores.
What Happens During the Conversion Process at the Optometrist or Optician?
An optometrist or optician will:
- Review your contact lens prescription: They'll carefully examine all the details of your prescription, including the base curve and diameter.
- Perform a comprehensive eye exam: This is crucial even if you have a recent contact lens prescription. Your eyesight can change, and a thorough exam ensures accuracy.
- Measure your pupillary distance (PD): Accurate PD measurement is essential for optimal vision.
- Determine the appropriate glasses prescription: They will use sophisticated formulas and your base curve measurement to calculate the appropriate spherical equivalent for glasses. This takes into account the difference in lens-to-eye distance.
- Recommend the appropriate type of lenses: Based on your needs and vision correction requirements, they will recommend single-vision, bifocal, or progressive lenses.
What if I only have my old contact prescription?
It's important to note that using an outdated contact lens prescription can lead to inaccurate glasses prescriptions. Your eye condition might have changed significantly since your last eye exam. Therefore, it's essential to schedule a comprehensive eye exam with an eye care professional.
Is it Possible to Get Glasses Without a Formal Eye Exam?
No reputable optician or optometrist will create glasses from solely a contact lens prescription without performing a thorough eye exam. This is primarily due to safety and accuracy concerns.
In conclusion, while you can't simply convert your contact lens prescription to glasses yourself, the process with a professional is relatively straightforward. Remember to bring your complete and up-to-date contact lens prescription along with your pupillary distance for the best results. Always prioritize a comprehensive eye exam to ensure accurate and safe vision correction.
